1. Field of the Invention
The present invention relates in general to disk storage systems and more particularly, to a method and apparatus for providing positional information on a disk in a hard drive assembly.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of information. The information is typically recorded on concentric tracks on either surface of one or more magnetic recording disks. To facilitate the storage and retrieval of data in an orderly manner, disks are typically organized in blocks called sectors. These sectors are located on the disk by a set of unique specifiers called cylinder (or track), head (or side) and sector number. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads.
The movement of the actuator is controlled by a servo system, utilizing servo information recorded on one or more of the magnetic recording disks. By reading this servo information, the actual radial positions of the heads can be determined, and after comparison with the desired head radial positions, control signals can be sent to move the actuator accordingly. Servo information is typically stored on a disk in one of two ways. In the first, a dedicated servo system, a set of several tracks on the disk or the entire disk surface, is reserved exclusively for storing information associated with the characteristic of the particular drive. Such information includes servo parameters and read/write channel parameters. A servo head reads this information to provide a continuous signal indicating the position of the servo head with respect to the servo disk. In the second type of servo system, the embedded servo system, sectors of servo information are interspersed with sectors of data on each disk surface. As a read head follows the data track around, it regularly reads a fresh sample of servo information from each servo sector with which to control its position.
FIG. 1 illustrates a typical sector on a disk of a hard disk drive. As shown, a typical sector 10 has a preamble field 20 which includes automatic gain control (AGC) information and synchronization information, a servo address mark 22 which signifies the beginning of a sector, an index field 24 which indicates the beginning of the first sector of the track, an identification field 26 which includes identification bits, a head identification field 28 for identification of head location, a gray code field 30 that identifies the particular cylinder (tracks) of the sector, a servo bit field 32 which includes a number of servo bits A, B, C, D, and a data field 34 which contains the data. The servo bits A, B, C and D are used to maintain the read/write head on the centerline CL of a corresponding track. The identification field 26 typically includes an index bit and 7 bits of angular position information; the head identification field 28 typically includes 3 bits of data for identifying the head (or side) position of the disk pack and the gray code field 30 typically includes 13 bits of data for providing track identification. In conventional disk drives, absolute positional information is stored in graycode in the gray code field 30 of a particular sector 10. Due to power consumption, cost and throughput concerns, reduction of media space used in providing the servo information is highly desirable. However, most of the segments of the sector 10 are head and/or media dependent and reduction of these segments is difficult.
Accordingly, there is a need in the technology for a method and apparatus for providing servo information on a disk in a hard drive assembly while reducing the media space required for the provision of such information.